1. Field of the Invention
The present invention relates to an oscillator using a circuit board of a glass epoxy resin, and particularly relates to an oscillator that relaxes strain on solder and improves heat cycle resistance performance.
2. Description of the Related Art
[Prior Art]
Conventionally, there is a crystal oscillator that uses a glass epoxy resin in a circuit board. Metal electrode patterns are formed on the circuit board, and an electronic component of ceramic or the like is mounted on the electrode patterns by soldering.
[Conventional Crystal Oscillator: FIG. 22]
A conventional crystal oscillator is described below, with reference to FIG. 22. FIG. 22A is a plan view of the conventional crystal oscillator, and FIG. 22B is a section view of the conventional crystal oscillator.
As shown in FIG. 22, in the conventional crystal oscillator, metal pattern wires 4 are formed on a circuit board (board) 1 of a glass epoxy resin, and an electronic component 2 having two terminal electrodes 3 is mounted on the board 1. For example, the electronic component 2 is a crystal resonator, a resistor, or the like.
In particular, the terminal electrodes 3 and the pattern wires 4 are bonded by solder 5.
[Another Conventional Crystal Oscillator: FIG. 23]
Another conventional crystal oscillator is described below, with reference to FIG. 23. FIG. 23 is a section view of another conventional crystal oscillator.
As shown in FIG. 23, in another conventional crystal oscillator, metal land patterns (electrode patterns) 4 and a solder resist 8 are formed on an epoxy resin board 1, and a circuit component (electronic component) 2 is mounted on the electrode patterns 4.
In detail, component electrodes 3 are formed on the electronic component 2 at parts connected to the land patterns 4, and the component electrodes 3 and the land patterns 4 are fixed by mount solder 5.
[Related Art 1]
Related prior art includes Japanese Patent Application Laid-Open No. 2004-200187 “Printed-Wiring Board” (Nikon Corporation) [Patent Document 1], and Japanese Patent Application Laid-Open No. 2007-104005 “Surface Mount Crystal Oscillator” (Nihon Dempa Kogyo Co., Ltd.) [Patent Document 2].
[Related Art 2]
Related prior art includes Japanese Patent Application Laid-Open No. H11-135674 “Semiconductor Device and Manufacture thereof” (NEC Kansai, Ltd.) [Patent Document 3], Japanese Patent Application Laid-Open No. 2000-332396 “Mounting Structure of Electronic Components” (Alps Electric Co., Ltd.) [Patent Document 4], and Japanese Patent Application Laid-Open No. 2008-238253 “Pb-free Soldering Material, and Manufacturing Method of Semi-conductor Mounted Structure using the same” (Hitachi, Ltd.) [Patent Document 5].
[Related Art 3]
Related prior art includes Japanese Patent Application Laid-Open No. H07-231237 “Multiple Mode Crystal Vibrator and Crystal Vibrator” (Nihon Dempa Kogyo Co., Ltd.) [Patent Document 6], Japanese Patent Application Laid-Open No. H10-051263 “Crystal Vibrator” (River Eletec Corporation) [Patent Document 7], and Japanese Patent Application Laid-Open No. 2003-037441 “Piezoelectric Device and Electronic Equipment” (Seiko Epson Corp.) [Patent Document 8].
[Related Art 4]
Related prior art includes Japanese Patent Application Laid-Open No. 2005-203525 “Power Semiconductor Device and Method of Manufacturing Metal Base Plate” (Mitsubishi Electric Corporation) [Patent Document 9], Japanese Patent Application Laid-Open No. 2007-089003 “Piezoelectric Component” (TDK Corporation) [Patent Document 10], and Japanese Patent Application Laid-Open No. 2010-087145 “Electronic Component Mounting Substrate” (FDK Corporation) [Patent Document 11].
Patent Document 1 discloses that a columnar projection is provided at an electrode land where a solder ball bump is joined, and stress in a traverse direction is absorbed not only by an interface between the solder ball bump and the electrode land but also by a side surface of the projection.
Patent Document 2 discloses that, in a surface mount oscillator in which a crystal resonator and a mount substrate are joined, a projection is formed at connection terminals of the mount substrate in the case of joining the connection terminals of the mount substrate and resonator terminals of the crystal resonator by solder.
Patent Document 3 discloses a semiconductor device in which a semiconductor pellet having fine-pitch bump electrodes can be connected to a wiring board by forming a wide solder feeder on a fine conductive pattern.
Patent Document 4 discloses an electronic component mounting structure in which an insulation layer for coating an adhesive for temporarily fixing electronic components is formed in regions for mounting the electronic components so as to be thicker than a circuit pattern, so that a predetermined gap is formed between bottom faces of the electronic components mounted on the insulation layer and the circuit pattern.
Patent Document 5 discloses that a solder paste in which a Sn—Zn solder powder and a Sn powder or Zn powder having a higher melting point than the Sn—Zn solder powder are mixed is used as a soldering material, to suppress component inclination and secure soldered part thickness when mounting low heat-resistant leadless components.
Patent Document 6 discloses a structure in which a crystal chip is fixed to two support sections using a conductive adhesive on a substrate to supply a voltage from the support sections to the crystal chip, and a common lead electrode formed on a side of the crystal chip not fixed to the support sections is connected to a shield electrode formed on the substrate by wire bonding.
That is, a voltage is supplied from the two support sections on the substrate side to the crystal chip, and the common lead electrode on the opposite side of the crystal chip is connected to a ground level by wire bonding.
Patent Document 7 discloses that, in a crystal vibrator having horizontally arranged crystal vibrator bars, each crystal vibrator bar is supported only at one end while the other end is kept free, thereby eliminating stress on the crystal vibrator bars.
Patent Document 8 discloses a structure in which an IC chip is mounted in a package and an electrode on an upper surface of the IC chip and an electrode on a second layer are connected by a bonding wire.
Patent Document 9 discloses that, in a metal base plate, a low linear expansion material having an expansion coefficient equivalent or close to that of an insulating substrate is arranged at least at areas corresponding to four corners of the insulating substrate, to relax shearing stress by heat cycle and suppress a solder crack in a solder joining part between the insulating substrate and the metal base plate.
Patent Document 10 discloses that a piezoelectric unit formed by laminating a base substrate, a piezoelectric substrate, and a top plate in sequence and a printed board in which the piezoelectric unit is mounted by soldering satisfy specific conditional expressions regarding linear expansion coefficients and also Vickers hardness and maximum distortion of the base substrate are specified to thereby suppress a solder crack.
Patent Document 11 discloses that, by providing a ceramic sheet (strain suppressing body) on a top surface or internal surface of a printed wiring board facing an electronic component, a difference in expansion between the electronic component and the printed wiring board due to a temperature change near the electronic component can be reduced, resulting in a reduction in stress applied to a fillet of solder.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-200187
[Patent Document 2] Japanese Patent Application Laid-Open No. 2007-104005
[Patent Document 3] Japanese Patent Application Laid-Open No. H11-135674
[Patent Document 4] Japanese Patent Application Laid-Open No. 2000-332396
[Patent Document 5] Japanese Patent Application Laid-Open No. 2008-238253
[Patent Document 6] Japanese Patent Application Laid-Open No. H07-231237    [Patent Document 7] Japanese Patent Application Laid-Open No. H10-051263
[Patent Document 8] Japanese Patent Application Laid-Open No. 2003-037441
[Patent Document 9] Japanese Patent Application Laid-Open No. 2005-203525
[Patent Document 10] Japanese Patent Application Laid-Open No. 2007-089003    [Patent Document 11] Japanese Patent Application Laid-Open No. 2010-087145
However, the above-mentioned conventional oscillator has a problem that, due to a difference in thermal expansion coefficient between the electronic component (circuit component) using ceramic or the like and the glass epoxy resin circuit board, strain concentrates on the mount solder in a use environment where a heat cycle occurs, causing a crack in the solder.
It is commonly known that a solder crack is more likely to occur in large components than in small components.
However, certain circuit components cannot be reduced in size because of their performance or constants, and so there are many cases where large circuit components need to be used.
Especially in an oven controlled crystal oscillator (OCXO), in a use environment where power on/off is repeated, a temperature change from an ambient temperature to an oven control temperature (e.g. 85° C.) is added at each instance of power on/off, which induces a crack in solder. Thus, there is a problem with long-term reliability.
Note, Patent Document 1 discloses that an electrode land provided with a projection and an electrode facing the electrode land are joined by a solder ball bump, where the electrode land and the facing electrode are not in contact. Though a force in a traverse direction is addressed, solder strain due to a difference in thermal expansion coefficient between the electrode land and the facing electrode is not taken into consideration.
Patent Document 2 discloses that connection terminals provided with a projection are connected to resonator terminals by solder. Here, the resonator terminals and the connection terminals are made of the same tungsten, and therefore solder strain due to a difference in thermal expansion coefficient between both terminals is not taken into consideration.
Patent Document 3 discloses that a solder feeder for easing solder feed is provided on a conductive pattern formed on a board, but does not disclose a structure in which a thickness of a land pattern as an electrode is exploited to lift an electronic component with respect to the land pattern so as to create, between the land pattern and a component electrode formed on the electronic component, a space in which solder can be easily filled.
Patent Document 4 discloses that an insulation layer having coating zones for coating an adhesive for temporarily fixing electronic components is formed to create a gap between a circuit pattern and the electronic components. Here, the dedicated insulation layer needs to be formed in order to lift the electronic components. Thus, Patent Document 4 fails to disclose a structure of easily lifting the electronic components by exploiting a normal circuit board manufacturing process.
Patent Document 5 discloses that a metallic spacer is formed on a pad on a mount substrate and a semiconductor element is mounted and soldered at a gap portion, but does not disclose a structure of increasing the amount of solder in soldering between an electrode pattern on the substrate and a component electrode of the electronic component to form a fillet, thereby strengthening adhesion.
Patent Document 6 discloses that a crystal chip is fixed to two support sections on a substrate, and so does not address substrate expansion and contraction caused by a temperature change.
Patent Document 7 merely discloses a structure of supporting each crystal vibrator bar only at one end. Patent Document 8 merely discloses a structure of connecting an IC chip fixed in a package and an electrode on a second layer by a bonding wire.
Patent Documents 9 to 11 disclose techniques for suppressing a solder crack. However, these techniques require complex conditions and structures, and are unable to suppress a solder crack caused by a temperature change by a simple structure at low cost.